Optical fiber connectors and splices (hereinafter referred to collectively as "connectors") are an essential part of substantially any optical fiber communication system. For instance, connectors may be used to join segments of fiber into longer lengths, or to connect fiber to active devices such as radiation sources, detectors, or repeaters, or to passive devices such as switches or attenuators.
A novel optical fiber connector is disclosed in U.S. patent application Ser. No. 527,341, filed Aug. 29, 1983 by T. D. Mathis and C. M. Miller (Mathis herein), and assigned to the assignee of the instant application. The above patent application, incorporated herein by reference, discloses an optical fiber connector that utilizes two drawn glass capillary cylinders that serve to hold the two fiber ends and allow alignment of the ends by means of a simple alignment sleeve. The disclosed connector serves completely satisfactorily with multimode fibers, for which, due to their relatively large core diameter, alignment to within a few .mu.m is generally acceptable. The connector has also been found to frequently give satisfactory results with single-mode fibers. However, we have observed that it is not always easy to achieve very-low loss connections, that is, connections having a loss of the order of 0.1 dB or less, with the connector as disclosed.
Making single-mode connections typically involves active alignment of the fiber ends. Prior art methods typically comprise translating one fiber end relative to the other, typically by means of a precision stage, until maximum energy coupling across the gap is observed, typically by means of a remote detector. As will be appreciated, such a delicate procedure is both difficult to carry out in the field and requires highly skilled personnel.
Single-mode fiber connections can be quite easily made by means of the Mathis drawn glass connector, since at least a relative coupling maximum can be achieved by mere manual rotation of one of the capillary cylinders with respect to the other. Relative rotation of the two capillary cylinders typically changes the relative position of the fibers held within the capillaries, since the capillary bore typically is not rigorously concentric with the outer cylinder surface, the reference surface. Furthermore, the fiber may not be rigorously centered within the capillary, and the fiber core may not be concentric with the fiber. If the total eccentricities of the two fiber ends to be joined are identical or at least very nearly so, then a low-loss connection can be achieved by merely rotating, within the alignment sleeve, one capillary cylinder with respect to the other, until maximum coupling is observed. This is very often possible with mated capillary cylinder pairs, i.e., cylinders originating from adjacent parts of the same drawn glass capillary tube. However, even with mated pairs it is not always possible to achieve connections having losses less than 0.1 dB, since achievement of such a low-loss level typically requires alignment of the fiber ends to within less than about 1 .mu.m.
Because of the great advantages offered by the drawn glass or other "ferrule-type" fiber connectors, including low cost, simplicity, environmental stability, and versatility, a connector that uses drawn glass (or other) capillary cylinders and can consistently result in very low-loss single-mode fiber connections would be of considerable importance. This application discloses such a connector that, furthermore, is relatively simply and easily installed in the field, does not require expensive precision alignment apparatus, is rugged, and has good temperature cyclability.